Posted
by
timothy
on Thursday August 11, 2011 @12:42PM
from the shout-faster dept.

x_IamSpartacus_x writes "DARPA says contact with its experimental hypersonic glider was lost after launch from Vandenberg Air Force Base on the central California coast. The agency says in Twitter postings that its unmanned Falcon Hypersonic Technology Vehicle-2 was launched Thursday atop a rocket, successfully separated from the booster and entered the mission's glide phase. The agency says telemetry was subsequently lost, but released no details."

In what way is this bothersome? The reliability, or the brevity? We aren't exactly part of the command and control or decision making process you know. I'm sure there will be detailed releases forthcoming, but little bits of accurate information sooner is better than nothing.

I don't understand. You have to follow a person on Twitter in order to see their twitter posts, right? So if this audience of millions isn't interested in DARPA, why would they follow DARPA on twitter?

I don't understand. You have to follow a person on Twitter in order to see their twitter posts, right? So if this audience of millions isn't interested in DARPA, why would they follow DARPA on twitter?

They're already following other people on Twitter. They aren't reading RSS feeds. Thus, seeing what DARPA is up to on Twitter fits with their existing workflow.

The LA Times headline is, "Test of hypersonic aircraft fails." Now let's look at it from the perspective of an engineer, not a drive-by journalist. The first flight sent back nine minutes' worth of telemetry. Today's test transmitted telemetry for 20 minutes. That's a 122% improvement. Any engineer would be happy to get credit for that accomplishment!

They have probably forgotten about the doppler effect and are surprised it vanished from radio contact. Also: it's going Mach 20. You look up, go "HOLY SHIT!" while the earth shakes from the sonic boom, and wonder if you saw something flicker for 1/1000 of 1 second.

Plasma. Seriously. At that speeds (above Mach 10 I believe), a cone of plasma forms around the aircraft like it does in re-entry of spacecraft and plays major havoc with telecommunications. By which I mean it prevents it unless you design the craft very carefully. Hence, this test.

They have probably forgotten about the doppler effect and are surprised it vanished from radio contact.

Yes. A team of engineers would never think of that. That must be it.

Also: it's going Mach 20.

That would be a really big concern for a radio signal traveling at the speed of light. Yes, that puny Mach 20 would really put a hurtin' on that.

We better check the spectral lines of that radio signal to make sure it wasn't redshifted. It may have fallen into a black hole. That's much more likely than something going wrong in an experimental craft produced by a government project.

That would be a really big concern for a radio signal traveling at the speed of light. Yes, that puny Mach 20 would really put a hurtin' on that.

This is Mach 20 around 15,000MPH. Low earth orbit objects travel around 16,000mph, and radio operators must account for doppler shift for anything in the FM band or higher. The higher the frequency, the more significant the doppler shift.

So, for example, pointing an FM radio at the ISS and expecting to set the radio on the ISS to the same frequency to communicate just won't work. We now have a non-orbital object that's just getting into that sort of range of speed.

Frequency modulation would get mashed up some by a shift in frequency, so you'd expect amplitude modulation to work better, yes, at least from that perspective. Most space communication systems use pulse modulation for greater reliability over a highly unreliable and noisy environment. A final option, provided that the aircraft starts high enough up, is to have a black box-style recorder that can detect if it has been released from a functional aircraft or has fallen out of something breaking up at high spe

And the propagation speed of the radio waves is 671 million compared to that 15,000mph. Of course Doppler correction isn't necessary if you're looking at it sideways and not in front of or behind the moving object.

The Huygens mission to Titan would have been essentially lost if it weren't for one guy (Popken IIRC) who had a hunch that the Doppler shift wasn't correctly set up for receiver testing, and has done additional testing on the system while it was still enroute with Cassini to Saturn.

The Huygens telemetry receiver was based on a design that had operated successfully on several earlier space missions. That receiver was able to cope with a Doppler shift at data rates of up to 2 kilobits per second (Kb/s). The data rate between Huygens and Cassini, however, was 8 kb/s—four times faster.

Due to an implementation error, a scaling parameter in the Huygens receiver’s embedded software was not adjusted to accommodate the higher data rate. As a result, the bandwidth of the receiver’s bit synchronizer was too narrow to compensate for the Doppler shift of the data stream frequency.

What about engineers messing up units of measure, resulting in a loss of $300M mission:

The MCO MIB has determined that the root cause for the loss of the MCO spacecraft was the failure to use metric units in the coding of a ground software file, “Small Forces,” used in trajectory models. Specifically, thruster performance data in English units instead of metric units was used in the software application code titled SM_FORCES (small forces). The output from the SM_FORCES application code as required by a MSOP Project Software Interface Specification (SIS) was to be in metric units of Newtonseconds (N-s). Instead, the data was reported in English units of pound-seconds (lbf-s). The Angular Momentum Desaturation (AMD) file contained the output data from the SM_FORCES software. The SIS, which was not followed, defines both the format and units of the AMD file generated by ground-based computers. Subsequent processing of the data from AMD file by the navigation software algorithm therefore, underestimated the effect on the spacecraft trajectory by a factor of 4.45, which is the required conversion factor from force in pounds to Newtons. An erroneous trajectory was computed using this incorrect data.

Lol! Nice one bluefox! Yeah that's one expensive bottle rocket they just lost. I can't even imagine what the advanced electronics components required for those speeds cost to develop alone? As they sure as hell didn't come from Radio Shack!

Eh, it's not a lot of speed. Accounting for doppler shift at higher frequencies than FM band (around 2M the problem starts, but anything in VHF or above is going to get wide-band distortion) would require computer equipment. Actually controlling the plane? Zilog Z80 and a hard real-time microkernel OS. Think like Minix, then you strip out most of the useless crap, add a few small bits of specialized crap, and then add all your control programs to run under that. This is not stock Minix or QNX off the s

It would be rather freaky to see the machine fly past before you finished building it.

I know you're joking, but it provokes serious thought (if one should call any talk of time travel "serious").

If time travel were possible, and if it were possible for humans to access such travel, then surely we would only need to start the project and bang, a person from the future would show up and tell us to stop because of all the damage it caused in their future time.

Skynet has taken it...getting tooled up for the fight....when the Falcon hits the ground at Mach 20, the target will get obliterated. If you are named Connor, and are in the phone book, and live anuwhere near Vandenberg, now's the time to Get Moving.

On a more serious note, it's interesting that communication with the craft seems to be the most difficult part of the project (or at least the outer skin of the onion of problems involved with hypersonic flight). I would very much like to find technical papers written on this problem -- clearly, they thought they had it solved, but also just as clearly, they haven't. What's going wrong?

Touché: I was considering the problem of steady-state gliding at hypersonic velocities -- something I guess even theoretically you can only do as you approach the Kármán line [wikipedia.org] -- but you're right, in transient deceleration it's been done early and often.

Yes, exactly, but without the luxury of squishy humans on board to steer. If you want to fly it from the ground you've got signal lag and the minor problem of that plasma shroud. I would imagine it's autonomous in most ways, in some ways it is a bigger challenge than Shuttle.

I know plenty of people claim that the rifling of modern firearms causes the bullet to curve upwards, and that this could kinda-sorta be considered "gliding" but:

1. I've recently come to the conclusion that this is probably a myth, and
2. Even if it's not a myth, it's kinda pedantic to consider that "gliding".

It is a myth. Rifles are "zeroed" so that a bullet fired from the rifle will hit a target that's centered in the scope at a specified distance from the shooter. For example, the U.S. Army routinely zeroes their M-4s and M-16s for 300 meters, which means the bullet drop distance due to gravity is accounted for, and a target at 300m that the shooter is aiming in the center of his sights will be struck.

That's why bullets rise when they come out of a rifle. The barrel is pointed slightly upwards to give it t

So, apparently this hypersonic glider is part of the "Prompt Global Strike" concept, designed to deliver an explosive anywhere on earth in under an hour, for various purposes.

Now, we already have ICBMs that can do that; but we can't use those because ICBMs are typically equipped with thermonuclear warheads, which makes the world pretty jumpy about anybody launching one.

So, we are developing this rocket-boosted hypersonic glider thing that doesn't actually work yet to do it instead.

Here is what I don't understand: Is there anything about this new strike vehicle that would preclude a nuclear warhead in place of the conventional one? If so, it must have pretty serious payload limitations. If not, why would we expect global opinion to be any cheerier about this new toy than about the old one? Is it simply designed to be less visible to sensors than an ICBM?

I am a little skeptical that the current ICBMS are even that reliable. They have been sitting in their silos for 30+ years. I think the Russians actually predicted they would have a 30% - 40% failure rate so that's why they made so many to begin with and I guess the US followed suit.

The root of my puzzlement(and, unless their is in fact a reasonable explanation that escapes me, my dismay at this waste of money) is that, if the new system cannot either achieve sensor stealth sufficiently good that early-warning systems don't notice it, or prove to the diplomatic satisfaction of everybody who would get all 'second-strike'-y if they saw a US ICBM zipping off to an urgent appointment with something, then it represents absolutely no improvement over cheaper, actually working, hardware with

The problem with ICBMs, as far as I'm aware, is that they are Ballistic. This thing can presumably maneuver in the atmosphere and therefore hit smaller or moving targets. I'm not sure what the current state of ICBMs are, but if all the aiming is done in the boost phase then you're probably aiming at something the size of a city, while this thing could hit a city block or maybe a house.
Disclaimer: The above is all speculation on my part.

if all the aiming is done in the boost phase then you're probably aiming at something the size of a city, while this thing could hit a city block or maybe a house.

Well, in theory, we have exceedingly accurate ICBMs.

But you mentioned something important: Moving targets. Part of the problem with an ICBM is that it's good at hitting military installations which don't move around very much. But suppose you have a mobile launcher? Something like this could conceivably be launched and have it's course corrected.

But even ignoring that for a moment, I see nothing but good things coming from this research and the money spent thereupon. If they can figure it out for a mis

Your presumption is based on this being a near-final design. They're working on the physics of hypersonic craft, and once they get that worked out, they can start figuring out how to design an actual delivery system. A likely final version would be launched by a bomber, not a rocket, and look more like a large cruise missile, at least at weapon release. This keeps the bomber even further outside of enemy territory (or even the territory of friends of the enemy).

I believe the idea is that it can manuever to avoid whatever countermeasures an enemy may posses. Ballistic missles are launched on and designed to stay on a set trajectory that can not be changed in flight on a split second basis while keeping the same target.

You can re-target in-flight, not practical with ICBM. It doesn't have a launch signature to be confused with ICBM. It's larger hence more visible to modern sensors than an ICBM, so countries who matter will know the difference.

It's fast enough to appear to head in one direction then fly a sudden dogleg or other attack profile and defeat conventional defenses.

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a brilliant high speed fireball was seen crossing the horizon during the test, and littering the ocean with fine debris. DARPA has thus far refused to acknowledge any connection with today's test, and is still in the process of "processing telemetry data".

So. What would it look like if we found it, and in what general area might we find it. I guess there's a good chance it went into the ocean, which is tough. OTOH, maybe it could have spiraled in towards land. There's an awful lot of state park, national park, and BLM land in california. It'd be quite a find for somebody hiking in the desert, if they knew what they had just found was something other than ordinary aircraft wreckage or part of an old jeep that somebody set on fire.

This plane is pretty cool, but it is a waste of money. It's not working, it costs $BILLIONS, and its "justification" is to rush nukes to some WWIII target. There is no reason at all to spend this money on it. It's nothing but military corporate welfare.

But instead Americans will have to kiss goodbye our pensions and old-age healthcare. How goddamn stupid.

Three astronauts flying the X-20 DynaSoar into space for the first time disappear from radar on a test flight, then reappear. Serling's voiceover is spoken showing the ship represented in a hangar by a canvas-covered form.

However, all is not as it seems upon their return to Earth. After they land, Gart is sent to the hospital with a broken leg. During the evening the other two, Forbes and Harrington, go to a bar. There, Harrington suddenly gets a strange feeling as if he no longer belongs in the world. He immediately goes to a phone booth to call his parents, but they tell him they have no son. Then Harrington mysteriously disappears, and no one but Forbes remembers his existence. Forbes tells his story to Gart, who says he does not know any person named Harrington. Then Forbes looks in the mirror, only to find there is no reflection and runs out of the room. By the time Gart gets up to run after him, Forbes has mysteriously disappeared too, and nobody remembers him. Then Gart himself mysteriously disappears, and the ship does too -- wiping them off the face of the Earth.

Yeah, it's too bad that the glider was carrying all known copies of the information about how to build it, and all of the people who developed that information, and all of the people who taught them the principles involved, and all of the congresscritters that funded it. Dang, how much payload did that thing have, again?